Project: RS2 ABY

[prj]

i have heard so many times this thing about if you dont have a 3inch exhaust you cannot make more than 450hp or etc so i just dont believe it to be that serious anymore. It could be easier to make more power but as always i hate absolutes and i have proven them in the past a few times.

What exhaust did Ross's rs2 have? he uses the same turbo/setup roughly doesnt he? If i recall he made similar numbers when his car was working properly. If milltek, then that is definitely a 3inch full exhaust as i used to have one.

I just posted you the same car with 2.5" vs 3" exhaust and 430hp vs 510hp with the only thing changed being the exhaust.
What is your problem? Which part of 2 bar backpressure do you not understand? We had a backpressure gauge on the dyno on both of these runs.

Ross' turbo and setup is nothing like Andy's car. Pointless comparison.

[Error404]

a 3" exhaust will flow 50% more than a 2.5 at any given pressure, which is not insignificant. Not to say that your 2.75" is restrictive, but it flows around 22% more than a 2.5" so....

[prj]

Could not have said it better myself. People have a trouble grasping the concept of cross-sectional area.

2.5" or 63.5mm - 3167 mm2
2.75" or 69.85mm - 3832 mm2 (21% bigger than 2.5")
3" or 76.2mm - 4560 mm2 (44% bigger than 2.5")
3.5" or 88.9mm - 6207 mm2 (96% bigger than 2.5")

It's a square increase. 2.5" will top out at around 430bhp on these, 2.75" around 520bhp, 3" around 650bhp, 3.5" around 850 bhp.
Of course this is just a rough mathematical multiplication. Timing also affects the power, so if you can run MBT you will get more out of the same amount of fuel-air mixture etc.

[Sonic]

Vas I have no idea why but my milltek cat-back apparently measures 2.5" diameter whereas I was always led to believe it was 2.75" - I'm still not too happy about this.

I'm pretty sure Ross has a 3" setup on his RS2 and we always meant to do a comparison between them both. His has a k26/27 hybrid similar but different to my kx500. Can't remember if his hot side is a 6cm2 or 8 but think it must be 8 like mine.

Everyone involved was always surprised mine dyno'd consistently at 431bhp / 600Nm, it should have made more top-end and you could see it choking. I just put part of it down to the cam setup and possibly inlet. I didn't consider for a second that my supposed 2.75" exhaust would be a restriction before 450bhp but upon revelation of its actual size me, Dmitri, Will and JP all collectively went "DOH!!!".

I'd have loved to just change the exhaust and see what the original setup would have made. I suspect more like 450-460bhp which is what I was originally expecting.

Given the anticipated power increases specifically targeted at the top with these latest upgrades it seemed clear even a 2.75" exhaust would begin to limit the flow and output as it's a fundamentally restriction to the flow rate and thus power output and efficiency of the engine.

If I'd have kept the 2.5" setup I fully expect all this work may have just resulted in a small 20bhp gain - that's an aweful lot of time, money and effort put in for a tiny reward all down to a flow restriction in the exhaust so it has to go.

Unfortunately Ross has never had his car properly running on the dyno to get any realistic figures, but from what we do know we expect his car to also have done around 420-430bhp. That's about spot on for his setup but clearly highlights mine was down on power.

[A80Avant]

Let me have any data logs of power runs on the road Andy and we shall find out what u are making.

I was too considering a 3 inch cat back silent though to see if I can get any increase in power but I have gone through the 'more power phase' to enjoy what you have phase. It's expensive enough!!! Haha

[Sonic]

Let me have any data logs of power runs on the road Andy and we shall find out what u are making.

Will do when i get the car back along with a few videos

You just want a 2k to redline run in 3rd and 4th?

[EspenW]

Will do when i get the car back along with a few videos

You just want a 2k to redline run in 3rd and 4th?

Depending on spool, etc. 4th will typically yield higher numbers for power and especially torque, since you get a better load on the engine, but 3rd will work fine, and you will bump the limiter at around 100mph instead of 125mph (depending on your rev limiter), so better in that regards.
Find a flat piece of freeway and do a pull in each direction (if possible)

Some interesting discussion on exhaust size vs. power potential. I will make a new thread on the topic.

[prj]

Ross has 3" exhaust, and turbo is completely different, smaller compressor and much smaller hotside. Engine is built differently as well.

[A80Avant]

I must have missed your turbo upgrade then as I thought you had roughly the same stuff.

[Sonic]

Originally we both had k26/27 hybrids from Richard, then mine was destroyed along with my engine failure and following a botched repair which also failed went with a new kx500.

[Sonic]

The side exit exhaust is unfortunately no more, but this work of art is going in its place...

[Lloyd]

Nice welding!

[Error404]

Beautiful
Just a single tail pipe?

[rynaqui]

That looks sweet

[Sonic]

Beautiful
Just a single tail pipe?

No - I couldn't deviate from the classic early-90s twin side tailpipe. It's iconic and fundamental to the look of the car